An equalizer in an optical system may be configured to implement feed-forward equalization (FFE) and/or decision feedback equalization (DFE). An equalizer including both FFE and DFE may be referred to as an FFE-DFE equalizer. The FFE-DFE equalizer may further implement a least mean square (LMS) algorithm for adapting the equalizer to the channel to equalize digital data signals communicated in the optical system. Specifically, the FFE-DFE equalizer may correct inter-symbol interference (ISI) in the electrical signals such as ISI resulting from multimode dispersion in multimode fibers.
The LMS algorithm may operate by iteratively implementing and evaluating equalization tap coefficients (tap coefficients) until an optimum set of tap coefficients is discovered. The optimization of the tap coefficients may be based on a transfer function. The LMS algorithm may self-adjust the transfer function based on a gradient of mean square error between a desired signal and the actual signal output by the FFE-DFE equalizer. In the optical system, the FFE-DFE equalizer may continuously update the tap coefficients based on received digital data signals to adapt for time varying channels.
An eye diagram may represent a digital data signal. In an optical system the eye diagram may be generated from a digital data signal communicated from an optical receiver. The eye diagram may be generated by repetitively sampling the digital data signal and plotting the sampled digital data on monitoring equipment such as an oscilloscope. The eye diagram may provide information of the digital data signal and the optical system such as channel noise, inter-symbol interference (ISI), performance of a transmitter, or some combination thereof within a particular signaling interval. Opening the eye generally refers to improving the eye diagram, which may occur through changing tap coefficients in an equalizer. An eye opening monitor (EOM) generally refers to a device or circuit that receives a digital data signal and analyzes signal quality based on the eye diagram or an approximation of an eye diagram as implemented by EOM circuitry.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one example technology area where some embodiments described herein may be practiced.